Heat-sensitive stencil sheet

ABSTRACT

A HEAT-SENSITIVE STENCIL SHEET COMPRISING A THIN POROUS SUPPORTING SHEET HAVING BONDED THEREON A HEAT-SHRINKABLE THERMOPLASTIC FILM COATED WITH A LAYER CONTAINING A RELEASE AGENT WHICH IS A SILICON RESIN OR AN ANIONIC SURFACE ACTIVE AGENT.

United States Patent O 3,745,05Q HEAT-SENSl'I'iVE STENCIL SHEET Keishi Kubo, Kanagawa-ken, and Kiyoshi Sakai and Kenjhi Ito, Tokyo, Japan, assignors to Ricoh Co., Ltd., Ohta-ku, Tokyo, Japan No Drawing. Filed Sept. 25, 1970, Ser. No. 75,781 Claims priority, application Japan, Sept. 29, 1969, 44/77,994 Int. Cl. B41c 1/14; B41111! 1/12; B44d 3/30 US. Cl. l61-165 8 (Zlaims ABSTRACT OF THE DISCLOSURE A heat-sensitive stencil sheet comprising a thin porous supporting sheet having bonded thereon a heat-shrinkable thermoplastic film coated with a layer containing a release agent which is a silicon resin or an anionic surface active agent.

BACKGROUND OF INVENTION This invention relates to a stencil sheet which comprises a thin porous supporting sheet, usually paper, having bonded on a surface thereof a heat shrinkable synthetic resin film which is coated with a release agent.

IStencil sheets for use in mimeographic printing are normally prepared by forming a thermoplastic film on a thin porous support. The support usually Weighs from about 8-15 g. per square meter and is formed mainly from natural fibers obtained from mitsumata, paper mulberry, manila hemp, and the like. Alternatively, it may be formed from a synthetic fiber such as rayon, vinylon, tetron, acrylic fibers, and similar materials. The heat shrinkable thermoplastic film is preferably one in which the heat shrinkage at 100 C. for one minute is from about 2.6 to 15% in both biaxial directions. A number of polymers are suitable for the purpose. copolymers of vinylidene chloride and vinyl chloride are especially useful.

To obtain a stencil such as is used in mimeographic printing from a stencil sheet, an original is superposed on the film bonded surface of the stencil sheet, the opposite surface of the stencil sheet is then exposed to electromagnetic waves including infrared waves. There is thereby effected a perforation of the thermoplastic film in those areas opposite the image areas of the original. When printing paper is superposed on the perforated plastic film surface of the resulting stencil and printing ink is applied to the opposite side of the stencil, the ink penetrates the porous support, passes through the perforated image areas and adheres to the surface of the printing paper. There is thus produced a mimeographic print carrying an image identical with the original.

While the exact phenomena involved in the course of the preparation of a stencil has not yet been fully clari-.. fied it appears that a stencil is produced in the following manner.

The infrared rays penetrate the stencil sheet including the porous support, any adhesive which may be used, and the thermoplastic film, and then impinge on the original. The impinging rays are absorbed in the image areas of the original and cause an increase in the temperature of such areas. The rays are not appreciably absorbed in the non-image areas so that there is only a minimal increase in temperature if indeed there is any increase in the non-image areas. There results therefore on the surface of the original a thermographic image manifesting fluctuations in the surface temperature of the various image and non-image areas of the original in response to the degree of absorption of infrared rays. The areas of elevated temperature in the thermographic image 3,745,059 Patented July 10, 1973 cause a softening and simultaneous heat shrinkage of the congruent areas in the thermoplastic film in the stencil sheet. As a result the central portion of the film opposite each image area is broken by fusion to thereby form a stencil having a surface film With a perforated image corresponding to the original image.

The process of preparing a stencil as broadly outlined above is quite staightforward when the correct amount of infrared radiation is utilized. However, it is quite difficult to control the quantities of such radiation which impinges on the original. As a result, an excessive quantity of radiation is often used and the amount of fusion of the thermoplastic film increases beyond the desired point. The excess melted film partially adheres to the image area of the original and thereby causes the original to be damaged when the stencil is separated therefrom. Additionally, the fused film is often transferred back to the perforated areas of the stencil sheet Where it solidifies and inhibits the passage of copying ink when the stencil is used for mimeographic printing. As a result of this phenomena there is an appreciable decrease in clar ity of the copy produced. When the original image is one which has been produced through off-set printing a further difliculty arises due to the fact that the thermoplastic resin contained in the off-set printing ink melts and transfers to the film bonded surface of the stencil and becomes adhered thereto. This causes damage when the stencil is removed from the original. Additionally, it may accumulate in the image areas and inhibit the passage of ink.

THE INVENTION It has now been discovered that stencil sheets having the desired properties to essentially alleviate the above defined problems-can be prepared by coating the thermoplastic film with selected release agents which are silicon release or anionic surface active agents.

The porous supports utilized in the invention are the same as those descibred above. The thermoplastic films are of the class usually employed for such purposes and include polypropylene, polyvinyl chloride, polyethylene, polystyrene, vinyl chloride-vinyl acetate copolymers and vinylidene chloride-vinyl chloride copolymers, for example.

The release agents utilized in the present invention substantially prevent the phenomena of thermo-adhesion discussed above and in this manner substantially alleviate the shortcomings of conventional sheets.

The release agents utilized in the invention are especially selected because of their following properties.

(1) There is substantially no absorption of radiation in the range of from 500-2000 millimicrons. Such absorption, if it takes place in the release agent, would generate heat and make it difficult, if not impossible, to obtain the desired thermographic pattern on the stencil sheet.

(2) The release agent should be a flexible solid at room temperature so as not to interfere with the release of the stencil from the original.

(3) It should soften in a temperature range of from about 60 C.200 C., heat-sensitive film is perforated. If it fuses at a temperature :above the perforation range of the thermoplastic film it will interfere with the perforation. If the release agent fuses at a temperature below the perforation range of the film it will soften or melt on the film on the nonimage areas and be transferred to the original.

(4) The release agent should have a low viscosity when melted. Otherwise it will hamper the contraction of the heat-sensitive thermoplastic film and make it impossible to obtain a clear perforated image.

i.e. in the range at which the (5) It should have a low fusion energy so as to limit the amount of energy required to perforate the heat-sensitive thermoplastic film.

Since the stencil sheets and stencils will be handled by operators in the usual printing operation the release agent should be non-toxic.

A limited class of compounds has been discovered which when used as release agents in the preparation of stencil sheets and stencils meet the above criteria. These include specifically selected silicon resins and anionic surface active agents.

The anionic surface active agents useful in accordance with the present invention include those having the Formulas (a) and (b).

General formula (a) R SO M wherein R represents a radical selected from the group consisting of alkyl radicals having from about to 30 carbon atoms; alkenyl radicals having from about 10 to 30 carbon atoms; radicals expressed by the formula wherein R is a radical selected from the group consisting of radicals having from about 8 to carbon atoms and alkenyl radicals having from about 8 to 25 carbon atoms; and radicals expressed by the formula N C O Rn,

wherein R has the same meaning as R; R" is a radical selected from the group consisting of hydrogen and alkyl radicals having from about 1 to 6 carbon atoms, and R' is a radical selected from the group consisting of alkylene radicals having from about 1 to 10 carbon atoms; and M represents a radical selected from the group consisting of potassium, sodium and ammonium radicals;

General formula (b) R OSO M wherein R represents a radical selected from the group consisting of alkyl radicals having from about 10 to carbon atoms; alkenyl radicals having from about 10 to 30 carbon atoms and radicals expressed by the formula wherein R' is a radical selected from the group consisting of alkyl radicals having from about 8 to 25 carbon atoms and alkenyl radicals having from about 8 to 25 carbon atoms; R is a radical selected from the group consisting of hydrogen and alkyl radicals having from about 1 to 6 carbon atoms; and R' is a radical selected from the group consisting of alkylene radicals having from about 1 to 10 carbon atoms; and M has the same meaning as above.

Specific examples of the compounds expressed by the general Formula (a), include such substances as sodium dodecane sulfonate (C H -S0 -Na), sodium 4-dodecyl benzene sulfonate (C H -C H -SO -Na), sodium triacontane sulfonate (C H -SO -Na), sodium 6-dodecene sulfonate (C H -SO -Na), sodium 15-triacontene sulfonate (C H -SO -Na), sodium 4-pentacosyl benzene 4 sulfonate (C H C H S0 Na), amino) ethane sodium sulfonate C1 H -CON'C H SOaNa IO-(N-hexyl-oleoylamino) decane sodium sulfonate |Jo 1s H as- N- m zoSOaNa 2-(N-methyl-stearoylamino) ethane sodium sulfonate v Cr7H35.CON-C;H SO3N& and 10-(N-hexyl-stearoylamino) decane sodium sulfonate Ca u GnHss- C ON- C1o 2u S s a and an of them are suitable. All of these compounds, which for purposes of illustration are shown as sodium salts, can be used in this invention. Other salts such as the potassium salt and the ammonium salt may also be used.

Typical examples of the compounds expressed by the general Formula (b) include such materials as sodium dodecyl sulfate (C H -OSO -Na), sodium triacontyl sulfate (C H -OSO -Na), sodium fi-dodecenyl sulfate (C H -OSO -Na), sodium lS-triacontenyl sulfate so se' s' Z-(N-methyl-oleoylamino) ethyl sodium sulfate CH3 (C17H33- C OI1I- CzH4- 0 S O Na) and IO-(N-hexyl-oleoylamino) decyl sodium sulfate OeHia and any of them are suitable. As with the compounds of general Formula (a), salts other than those illustrated can be used.

The above described anionic surface active agents not only are possessed of the desired physical and chemical properties discussed in detail herein, but also have additional advantages in that they are readily soluble in water and sufiiciently inexpensive to be used in the manufacture of stencil sheets.

The silicon release agents useful in this invention include linear and cross-linked polysiloxanes with a viscosity of from about 5,000 to 500,000 cp. (centipoises) at 25 C. The preferred silicon resin release agents for use in the present invention have the structural unit wherein any one of X and Y is hydrogen, alkyl having from about 1 to 4 carbon atoms, phenyl or hydroxyl radical, and at least one of the remaining bonds is combined with oxygen of another structural unit. This is, it has a structure such, for instance, as follows:

2- (N-methyl-oleoyl- Typical examples of the silicons effective in preventing said thermal adhesion in accordance with this invention include those substances useful as releasing agents or paper processing agents. They include, for instance, those manufactured by Shinetsu Chemical Ind. Co., Ltd. sold under the trade names Shinetsu Silicon Releasing Agent- KS707 (a varnish-type silicon releasing agent) and 3 Shinetsu Silicon Releasing Agent KM 763 (an emulsiontype silicon releasing agent), and the product of Toray Silicon Co., Ltd. sold under the trade name Toray Silicon SH 490 (an emulsion-type silicon releasing agent), and Union Carbide R-63 Silicon Resin.

Among the commercial anionic surface active agents based on sodium dodecyl benzene sulfonate, there may be mentioned Ncoplex No. 6 (the trade name of a manufacturer of Kao Atlas Co., Ltd., Japan), NACCONOL NR (the trade name of a manufacturer of National Aniline & Chem. Co., U.S.A.), IGEPEL NA (the trade name of a manufacturer of IG Farben Industrie, Germany), etc.

The amount of release agent useful in the preparation of the stencil sheets is normally from about 0.05 to 0.5 g. per square meter based on the dry weight of the stencil sheet. The efliciency of the stencil sheets is effected by the quantity of release agent employed. If an excessive amount is utilized the clarity of the perforated image is adversely affected. If too little is used the desired improvements in efliciency are not achieved. The optimum quantity for best results will vary somewhat amongst specific release agents but will generally be found Within the above disclosed range. The ideal amount for each agent may be readily determined by absorption.

As with the standard stencil sheets, the preferred thermoplastic film for use in this invention is derived from copolymers of vinylidene chloride and vinyl chloride, especially those in which the weight ratio of the former to the latter is from 80 to 95:20 to 5. The thickness of the film no matter what the identity of the thermoplastic resin, is typically from about 540 microns and the heat shrinkage in both biaxial directions when subjected to heating at 120 C. for one minute is from about 2.6l5.0%. A thermoplastic film having the desired properties can be obtained by molding and stretching the polymer and then subjecting it to heat treatment. For the vinylidene chloride-vinyl chloride copolymer mentioned above the heat treatment is normally effected at about 120 C. for 3-30 seconds.

The use of release agents for the purposes aforesaid has been investigated by others and sodium stearate has heretofore been suggested as a useful release agent in the preparation of stencil sheets. A most unexpected discovery in connection with this invention is that the release agents utilized in the invention and having the properties described above can be used in such low quantities when compared to the amounts of sodium stearate required to obtain the same results. The amount of sodium stearate normally recommended is about 1 g. per square meter, or about 100% above the higher end of the useful range for the release agents utilized herein. Moreover, even when used in the recommended quantities sodium stearate does not approach the thermo adhesion preventing efliciency of the release agents on this invention. One reason for the deficiencies of sodium stearate as a release agent and for the deficiencies of the stencil sheets prepared utilizing sodium stearate, is that sodium stearate begins to soften at about 50 C. and shows the maximum endothermic reaction at 150 C. That is to say, the endothermic curve for sodium stearate is very slow and ordinarily it does not possess the properties described above particularly under items l-S, that are possessed by the release agents utilized in this invention.

When stencil sheets in accordance witht this invention are compared with stencil sheets utilizing sodium stearate in the recommended quantities it is found that the thermoplastic filrn in the stencil sheets of the invention are rapidly perforated to form the perforation image while those employing sodium stearate form the perforated image much more slowly. This is an important commercial advantage of the products of this invention.

The release agents of this invention represented by general Formulas (a) and (b) are much more watersoluble than sodium stearate. Accordingly it is much easier 6 to dissolve the required amount in water for the commercial preparation of stencil sheets. The result is that the more concentrated solutions can. be used and the stencil sheets of the invention can be coated very rapidly on a commercial scale. The use of water as a solvent also decreases the cost of the product.

The silicon release agents of the invention also have particular advantages when compared with sodium stearate. They are generally immiscible with organic compounds and have a relatively low surface tension. Therefore, they do not mix with any organic compounds which may be present in the printing inks, for example to thereby interfere with the production of the stencil or the printing of the copies. The amount of silicon release agent employed is as described above and again is much lower than the amount of sodium stearate required for the same purposes. As with the anionic surface active release agents stencil sheets formed using silicon release agents are perforated rapidly. Additionally, silicon release agents have excellent water dispersibility as a consequence of which highly concentrated aqueous emulsions and dispersions can be produced and utilized for high speed production of stencil sheets.

For the preparation of stencil sheets in accordance with the invention a thermoplastic film, for example, a vinylidene chloride-vinyl chloride thermoplastic film, is bonded to the porous thin support utilizing, for example, any of the adhesives generally employed in the preparation of conventional sheets and illustrated in the examples. The release agent is then applied to the top surface of the film. Alternatively the release agent can be applied to the film and the film-release agent combination then bonded to the porous support.

The following non-limiting examples are given by way of illustration only.

EXAMPLE 1 A 7,u. thick film comprising a vinylidene chloride-vinyl chloride copolymer resin (component ratio :20) was subjected to heat treatment at C. for 10 seconds. Thus treated film was bonded to a 301i thick porous thin paper by means of vinyl acetate type adhesive (a methanol solution) and dried, whereby a standard heat-sensitive stencil sheet was prepared.

Subsequently, the film-bonded surface of said stencil sheet was coated with 1.0% n-hexane solution of a linear polysiloxane release agent having a viscosity of 10,000 cp. (Shinetsu Silicon Releasing Agent KS 707) and dried at a temperature about 40 C. to 50 C. The amount of release agent on the resulting stencil sheet was about 0.05 g. per square meter.

EXAMPLE 2 The film-bonded surface of the heat-sensitive stencil sheet prepared in Example 1 was coated with 10% aqueous emulsion of a linear polysiloxane release agent having a viscosity of 50,000 cp. (Shinetsu Silicon Releasing Agent KM 763) and subjected to the same treatment as in Example 1 to form a thermo-adhesion preventive layer. The amount of release agent was about 0.2 g. per square meter.

EXAMPLE 3 The film-bonded surface of the heat-sensitive stencil sheet as prepared in Example 1 was coated with 10% aqueous emulsion of a linear polysiloxane release agent having a viscosity of 100,000 cp. (Toray Silicon 81-1490) and subjected to the same treatment subsequent as in Example 1 to form a thermo-adhesion preventive layer. The amount of thermo-adhesion preventing agent on the film was about 0.4 g. per square meter.

Subsequently, for the purpose of comparing the efficiency of the kinds of heat-sensitive stencil sheets prepared in Examples 1 and 2 and the present Example 3 with that of a standard stencil sheet not coated with a.

release agent of this invention, an original newspaper was brought into close contact with the thermo-adhesion preventive coated surface of each stencil sheet and the stencil sheets were then subjected to radiation rich infrared rays applied from the paper side thereby effecting perforation congruent with the original image. The resultant stencil sheets were separated from the original, and utilized for printing on a rotary mimeographic press, with the following results.

In the case of the standard stencil sheet having no release agent coating, the areas of the original having thick capital letters or other large solid segments were damaged by accumulation of fused thermoplastic film from the stencil sheet. In the stencil itself the passage of the copying ink was inhibited with the result that the printed image did not perfectly reproduce the original image. The chief defect was the presence of blank spots in the printed image. Even in case of thin, small letters on the original, slight adhesions by fusion were observed with the result that the edges of the image were not perfect and there was a lack of sharp definition in the printed image and a deficiency in resolving power.

On the other hand, in case of the stencil sheets of Examples 1, 2 and 3, the separation of the original therefrom subsequent to application of the infrared rays was performed easily Without encountering the difficulties observed in the sample. There was no thermal adhesion whatever onto the original or perforated area. When the stencils were used for printing there was an extremely smooth flow of the copying ink. It was possible to produce more than 2000 prints with extremely distinct images which faithfully reproduced the original.

EXAMPLE 4 A 7n thick film comprising vinylidene chloride-vinyl chloride copolymer resin (component ratio 80:20) was heat treated at 100 C. for 10 seconds. It was bonded to a 30p. thick porous thin paper using a vinyl acetate type adhesive (a methanol solution) and dried, to produce a standard heat-sensitive stencil sheet.

The film-bonded surface of the stencil sheet was then coated with a 15% aqueous solution of sodium dodecyl sulfate, stretched with an air-knife employing a static pressure of 300 mm.-H O, and dried at a temperature of about 40 C. to 50 C. The amount of thermo-adhesion preventing agent was about 0.3 g. per square meter.

EXAMPLE 5 The film-bonded surface of the standard heat-sensitive stencil sheet of Example 4 was coated with aqueous solution of sodium dodecyl benzene sulfonate and subjected to the same treatment as in the case of Example 4, whereby a thermo-adhesion preventive layer was formed. The amount of the thermo-adhesion preventing agent was about 0.5 g. per square meter.

EXAMPLE 6 The film-bonded surface of the standard heat-sensitive stencil sheet of Example 4 was coated with an 8% aqueous solution of the ammonium salt of the ester of lauryl alcohol and sulfuric acid and subjected to the same treat ment as in Example 4 to produce a thermo-adhesion preventive layer. The amount of release agent was about 0.2 g. per square meter.

EXAMPLE 7 The film-bonded surface of the heat-sensitive stencil sheet of Example 4 was coated with 5% aqueous solution of oleoylamino ethane sodium sulfonate and subjected to the same treatment as in Example 4 to produce a thermo-adhesion preventive layer. The amount of the thermo-adhesion preventing agent was about 0.4 g. per square meter.

8 EXAMPLE 8 A 10% aqueous solution of the sodium dodecyl sulfate employed in Example 4 and 10% aqueous solution dodecyl benzene sulfonate were blended in equal amounts and coated on the surface of a standard heat-sensitive stencil sheet in the same manner as in Example 4 to produce a thermo-adhesion preventive layer containing about 0.5 g. per square meter of release agent.

Subsequently, for the purpose of comparing the elficiency of the heat-sensitive stencil sheets of Examples 4 through 8 with that of a standard stencil sheet not coated with a release agent, a newspaper was brought into close contact with the film side of the stencil sheets and the stencil sheets were then developed by the usual procedure. The resultant stencils were employed for mimeographic printing and the results compared. It was found that the stencils obtained from the stencil sheets of Examples 4 through 8 and the prints obtained from them were much superior to the sample stencil and the prints obtained from it in the same manner as described in Example 3.

What we claim is:

1. A stencil sheet comprising a porous supporting sheet having bonded thereon a heat shrinkable thermoplastic film the top surface of said film being coated with a thin continuous film containing release agents selected from the group consisting of silicone resin release agents and anionic surface active release agents, the said release agents being flexible solids at room temperature, heat fusible at a temperature of from about 60 C. to 200 C. and substantially non-absorptive of radiation in the range of from 500 to 2000 millimicrons.

2. A stencil sheet according to claim 1, wherein the anionic surface active agent is selected from the group consisting of compounds expressed by the following general Formulas (a) and (b):

General formula (a) R SO M wherein R represents a radical selected from the group consisting of alkyl radicals having from about 10 to 30 carbon atoms; alkenyl radicals having from about 10 to 30 carbon atoms; radicals expressed by the formula wherein R' is a radical selected from the group consisting of radicals having from about 8 to 25 carbon atoms and alkenyl radicals having from about 8 to 25 carbon atoms; and radicals expressed by the formula NGOR I General formula (b) R OSO M wherein R represents a radical selected from the group consisting of alkyl radicals having from about 10 to 30 carbon atoms; alkenyl radicals having from about to 30 carbon atoms and radicals expressed by the formula wherein R is a radical selected from the group consisting of alkyl radicals having from about 8 to 25 carbon atoms and alkenyl radicals having from about 8 to 25 carbon atoms; R" is a radical selected from the group consisting of hydrogen and alkyl radicals having from about 1 to 6 carbon atoms; and R' is a radical selected from the group consisting of alkylene radicals having from about 1 to 10 carbon atoms; and M has the same meaning as above.

3. A stencil sheet according to claim 1, wherein a main component of said silicone resin is polysiloxane having a structural unit expressed by the general formula:

wherein X and Y represent radicals selected from the group consisting of hydrogen; alkyl radicals having from about 1 to 4 carbon atoms, phenyl and hydroxyl.

4. A stencil sheet according to claim 1, wherein said thermoplastic film comprises a polymer selected from the group consisting of polypropylene, polyvinyl chloride, polyethylene, polystyrene, vinyl chloride-vinyl acetate copolymers and vinylidene chloride-vinyl chloride copolymers.

S. A heat-sensitive stencil sheet according to claim 4, wherein a. heat shrinkage of said film at 100 C. for one minute is in the range of from 2.6 to 15.0% in both biaxial directions.

6. A heat-sensitive stencil sheet according to claim 1, wherein the polymer comprises a vinylidene chloridevinyl chloride copolymer, wherein the Weight ratio of vinylidene chloride to vinyl chloride is in the range of from to parts by weight of the former to from 20 to 5 parts by weight of the latter.

7. A heat-sensitive stencil sheet according to claim 1, wherein the thickness of the film is from about 5 to 101k and a weight of the porous supporting sheet is from about 8 to 15 grams per square meter.

8. A heat-sensitive stencil sheet according to claim I, wherein an amount of release agent coated on the thermoplastic film is from about 0.05 to 0.5 gram per square meter.

References Cited UNITED STATES PATENTS 3,230,289 1/1966 Eder et a1 1177'6 P 3,258,443 6/1966 Cantor et a1. 117155 UA 3,264,243 8/1966 Knieriem 117155 UA 3,403,045 9/1968 Erickson et aI. 117-76 P 3,437,617 4/ 1969 Bogle 1l7167 3,483,020 12/ 196-9 Giellerup l17----3.4 3,558,881 1/1971 Gold 1l735.5 3,587,459 6/1971 Spencer 11735.5 3,619,345 11/1971 Kubo et a1 11735.5 X

GEORGE F. LESMES, Primary Examiner M. B. WITTENBERG, Assistant Examiner US. Cl. X.R. 

